An extracellular β-amylase, which was easily adsorbable onto raw corn starch, was purified 22.5-fold from a new isolate of Bacillus polymyxa No 26-1 with a Mr of 53 kDa and pI of 9.1. The optimum temperature was 45°C and pH 5.5 for raw corn starch. Thermal stability at 40°C and pH stability at 5.0-8.5 were shown. The degradation ofraw starch by β-amylase was greatly stimulated by pullulanase addition. Scanning electron micrographs revealed that starch granule degradation by the enzyme alone occured at the equatorial grooves of lecticular granules. Corn starch granules hydrolyzed by β-amylase had large holes on granule surfaces.